The measurement of organic carbon in a material sample provides information relevant to the hazardous nature of the material, if consumed, and possible contamination of the environment, if discharged. In a conventional process, acid is first used to generate carbon dioxide (CO.sub.2) from inorganic carbon. This CO.sub.2 is removed prior to oxidation of the residual organic carbon to CO.sub.2. CO.sub.2 from oxidation of organics is then measured.
A preferred oxidant for an aqueous solution including the remaining organic carbon compounds is potassium peroxydisulfate ("persulfate"), K.sub.2 S.sub.2 O.sub.8, for generating CO.sub.2. See, for example, Osburn and Werkman, "Determination of Carbon in Fermented Liquors," Ind. and Eng. Chem. 421 (1932); Menzel and Vaccaro, "The Measurement of Dissolved Organic and Particulate Carbon in Seawater," 9 Limnol. Oceanogra. 138 (1964). In a standard process for generating CO.sub.2 for carbon analysis, persulfate is provided with the sample for oxidation in a glass ampule and the ampule is sealed by melting the ends of the glass ampule. The sealed ampule is heated to promote the oxidation of organic carbon in the sample and the ampule is thereafter opened for CO.sub.2 measurement.
A principal disadvantage of the wet oxidation process is that a long reaction time is needed for an efficient oxidation with persulfate. A silver catalyst in the form of AgNO.sub.3 has been used to improve the reaction speed and to improve oxidation efficiencies. See, for example, Goulden and Brooksbank, "Automated, Determinations of Dissolved Organic Carbon in Lake Water," 47 Anal. Chem., 1943 (1975); Baldwin and McAtee, "Determination of Organic Carbon in Water with a Silver-Catalyzed Peroxydisulfate Wet Chemical Oxidation Method," 19 Microchem. J. 179 (1974). However, the AgNO.sub.3 is consumed in the reaction process and also greatly increases the rate of auto-degradation of persulfate. Further, the resulting solution contains silver ions and must be treated for environmental discharge purposes and/or for silver reclamation.
The prior art processes generally require attended and/or batch operation. If AgNO.sub.3 is not used, the reaction time is too great for any continuous operation. If AgNO.sub.3 is used, the supply must be replenished, the reaction waste treated and the AgNO.sub.3 freshly mixed with persulfate.
In many of the prior art analytical techniques the reaction occurs in sealed ampules of glass. It has been found that glass, while inert, contributes some carbon during CO.sub.2 generation, as indicated by "carbon blank", or test runs with zero carbon. The "carbon blank" values of glass are in the range of 1 microgram of carbon (".mu.g C") per ampule and these values limit the sensitivity of the analysis to about 2 .mu.g C per ampule.
Due to the nature of the solutions introduced into the reaction vessel, including acids and oxidants, material selections for the vessel are limited. A suitable material should not increase the carbon blank value, should not react with the analysis solutions and should be readily flushed between samples.
The above disadvantages of the prior art are overcome with the present invention wherein improvements in design and operation of a digestion vessel are provided for sample oxidation.